Taurine can be referred to as 2-aminoethanesulfonic acid and is one of the amino sulfonic acids found in the tissues of many animals. Taurine is an extremely useful compound because it has such pharmacological effects as detoxification effect, fatigue-relieving effect and nourishing and tonifying effect. As a result, taurine finds wide applications as an essential ingredient for human and animal nutrition.
Taurine is currently produced in an amount of over 50,000 tons per year from ethylene oxide and monoethanolamine. At present time, most of the taurine is produced from ethylene oxide, following a three-step process: (1) the addition reaction of ethylene oxide with sodium bisulfite to yield sodium isethionate; (2) ammonolysis of sodium isethionate to yield sodium taurinate; (3) neutralization with an acid, i.e., hydrochloric acid and, preferably, sulfuric acid, to generate taurine and sodium sulfate.
Although the ethylene oxide process is well established and widely practiced in industrial production, the overall yield is not very high, less than 80%. Moreover, the process generates a large amount of waste stream and sodium sulfate which is of little value and increasingly difficult to dispose of.
U.S. Pat. No. 8,609,890, incorporated herein by reference, discloses a cyclic process for the production of taurine in which sulfuric acid in the neutralization stage is replaced with sulfur dioxide or sulfurous acid. This cyclic process overcomes some of the disadvantages of the known ethylene oxide process by regenerating sodium bisulfite for its reuse in the addition reaction with ethylene oxide, thus eliminating the formation of large quantity of sodium sulfate as by product.
When the cyclic process is used in accordance with U.S. Pat. No. 8,609,890 for several cycles, impurities are found to accumulate to the extent that a new cycle has to be started. The overall yield for the cyclic process is still less than 85%.
It is an object of the present invention to overcome the disadvantage of the cyclic process in U.S. Pat. No. 8,609,890 for the production of taurine from ethylene oxide. The improved cyclic process can be carried out indefinitely and the overall yield is increased to greater than 90%, in particular, to 95%, and to nearly quantitative. This high yield is achieved by continuously converting the impurities, now identified as sodium ditaurinate and sodium tritaurinate, to sodium taurinate in the ethylene oxide process.
It is another object of the present invention to disclose a process for the effective separation of excess sodium sulfite from taurine, sodium ditaurinate, and sodium tritaurinate in the purge solution. Sodium ditaurinate, sodium tritaurinate, and unreacted sodium isethionate, present in the purge solution, are then converted to sodium taurinate.